The present invention relates to a fuel supply system of internal combustion engines, and more particularly to a fuel supply system having improved exhaust gas characteristics and operation performance of multi-cylinder combustion engines.
This type of known fuel supply systems of combustion engines employ a heater arranged in the intake passage of the engine for heating and evaporating the fuel injected into the intake passage so as to decrease deposition of the injected fuel on the inner surface of the intake passage and the intake valve, and hence the amount of hydrocarbons exhausted into the exhaust gas, and in addition improve the combustion in a cold engine during a startup. As an example, U.S. Pat. No. 5,894,832 discloses an internal combustion engine provided with a multi-point injection (MPI) system, in which fuel is injected from injection valves (referred to as port fuel injection valves) one for each intake port of each cylinder, and with an auxiliary air passage, upstream of intake passage, for bypassing a throttle valve. In this arrangement, the engine has a further fuel injection valve (referred to as upstream injection valve) provided near the suction ports and a heater in addition to the auxiliary air passage. The prior art engine is directed to prevent the fuel from deposition on the inner surface of the intake passage by injecting the fuel from the upstream injection valve towards the heater thereby facilitating evaporation of the fuel and hence preventing deposition of fuel on the inner surface of the intake passage during a warm run subsequent to a cold startup period.
The above technique may advantageously improve the combustion of fuel after a startup idling because of heater-assisted evaporation of the fuel in the intake passage. Hence, the technique may make the delay angle of ignition larger as compared with other types of conventional internal combustion engines not equipped with a heater in the intake passage, and may reduce carbon hydrates (HC) in the exhaust gas under warm operational condition (after a cold startup period).
This type of prior art engines have an additional fuel injection valve and a heater in the intake passage upstream of the fuel injection valve in proximity to the individual ports (in the intake passage or on the engine head) of the internal combustion engine, as mentioned above. It is noted, however, that on account of design limitations on the configuration of the suction pipe (intake passage) and/or the layout of the engine room, it is often the case that the additional fuel injection valve and the heater cannot be positioned adequately to distribute fuel evenly to each of the cylinders.
Consequently, it is often the case that the fuel-air ratios cannot be the same or maintained within an expected range for the cylinders (i.e. the fuel-air ratios differ for the individual cylinders).
In addition, uneven fuel-air ratios among the cylinders can spoil the operation performance of the engine.
In view of the above technical background, the present invention is proposed, of which objects are to provide a fuel injection system of internal combustion engines which can reduce fuel deposition on an intake passage wall of the engine, and to distribute fuel evenly to each of the cylinders of the engine, whereby improving its exhaust gas characteristics and operation performance.
Under the objects there is provided a fuel supply system of an internal combustion engine, comprising:
an intake passage;
a downstream fuel injection valve locating at a downstream position of the intake passage near the intake port of each cylinder of the engine; and
a controller, wherein
the intake passage is equipped with a fuel injection and evaporation device which has
an upstream fuel injection valve;
a heater for evaporating injected fuel; and
an air passage for supplying air to the injected fuel, and wherein
the controller is adapted to control amounts of fuel injected from the downstream fuel injection valve and the upstream fuel injection valve, thereby controlling the fuel-air ratio of the injected fuel.
Because of this arrangement, the inventive fuel injection and evaporation device provided in the intake passage advantageously reduces uneven distribution of fuel to the individual cylinders due to design limitations on the mounting location of the evaporator and on the configuration of the intake passage, thereby maintaining the fuel-air rations for the individual cylinders within a specified range.
More specifically, a fuel supply system of the invention comprises a controller having means for calculating the ratio of fuel amounts to be allotted between the upstream fuel injection valve and the downstream fuel injection valve (the ratio hereinafter referred to as fuel allotment ratio, and the means referred to as fuel allotment calculation means). The fuel injection allotment calculation means is adapted to allot less fuel to the downstream fuel injection valve than to the upstream fuel injection valve.
In this arrangement, amounts of fuel can be appropriately allotted between the upstream fuel injection valve and the downstream fuel injection valve, so that unevenness in the fuel-air ratio among the cylinders can be easily reduced. In another embodiment of a fuel supply system of the invention, the controller has means, one for each cylinder, for correcting the amount of fuel injected from the downstream fuel injection valve (said means referred to as fuel amount correction means), and a storage area (fuel amount correction map) for storing constant control parameters calculated by the fuel amount correction means.
The controller may utilize the constant control parameters stored in the storage area as described above to correct uneven fuel-air ratios among the cylinders. The correction can be done by calculating, in a predetermined task, corrective fuel amounts necessary to minimize the uneven fuel-air ratios based on the constant control parameters by means of the fuel amount correction means.
In a further embodiment of the invention, the controller has corrective fuel amount calculation means, one for each cylinder, for calculating a corrective fuel amount for each cylinder based on the actual fuel-air ratio and a target fuel-air ratio for the cylinder. The calculated corrective fuel amounts are stored in the storage area.
It is noted that such corrective fuel amount calculation means and the fuel amount correction map together may provide the controller with the same ability as the preceding controller adapted to calculate the corrective fuel amounts based on the constant control parameters stored in the storage area.